Stapled peptides are promising therapeutic candidates due to their enhanced stability and ability to target intracellular protein–protein interactions. Recent studies highlight the growing interest in electrochemical peptide modification as a mild and sustainable alternative to conventional stapling methods. Here, we present an electrochemical strategy for site-selective tyrosine modification using phenothiazine, with graphite felt (GF) as the anode and nickel (Ni) as the cathode. This method was successfully applied to the anticancer peptide p53, where phenothiazine was efficiently conjugated to tyrosine residues introduced at stapling positions. In peptides containing two tyrosine sites, conjugation occurred preferentially at the N-terminal residue, underscoring the inherent site-selectivity of this approach. The simplicity of the reaction setup, together with the use of inexpensive materials, further demonstrates its potential as a cost-effective alternative to traditional stapling techniques. Overall, this electrochemical approach provides a sustainable route to stapled peptide synthesis under mild conditions and broadens the applicability of peptide modification in drug development. By enabling the generation of stable and functional peptide therapeutics, it paves the way for new strategies in peptide drug discovery.